In the 3rd generation mobile communication Long Term Evolution (abbreviated as LTE) system, users need to initiate a detachment process in some cases (such as switch off) so as to release the resources occupied by a User Equipment (abbreviated as UE). Hereinafter, the detachment process in the situation that the users switch off will be described in detail.
If a UE currently needs to switch off, then a detachment process for switching off is initiated, and the used message name is Detach Request (Detach Type: switch off). After the UE sent out a Detach message, which is used for switching off, and waited for a certain machine time period, the UE does not need to wait for a Detach Accept message sent from core network (Evolved Packet Core, abbreviated as EPC) and can directly release the UE context locally.
After having received the Detach Request message, the EPC judges the subsequent processing procedure according to the Detach Type. When the Detach Type is switch off, the EPC does not send the Detach Accept message to the UE, but directly sends a UE CONTEXT RELEASE COMMAND message to an evolved Node Base (abbreviated as eNB), and carries an Information Element (abbreviated as IE) cause (IE Cause) in the UE CONTEXT RELEASE COMMAND message, wherein the particular cause is Detach. When receiving the UE CONTEXT RELEASE COMMAND message, the eNB itself releases resources locally and sends a Radio Resource Control (abbreviated as RRC) Connection Release message to the UE. FIGS. 1 and 2 will be taken as examples for description hereinafter:
FIG. 1 is a schematic diagram of the flow of a Detach process for switching off when a UE is under EMM_REGISTERED state & ECM_IDLE state according to the related art. As shown in FIG. 1, a wireless link (i.e. Radio Resource Control (abbreviated as RRC) connection process is established) and a logic 51 connection are firstly established, and then the detachment process for switching off is completed.
FIG. 2 is a schematic diagram of the flow of a Detach process for switching off when a UE is under EMM_REGISTERED state & ECM_CONNECTED state according to the related art. As shown in FIG. 2, the UE directly transfers messages via an uplink Non Access Stratum (abbreviated as NAS), i.e., the uplink (abbreviated as UL) Information Transfer sends a Detach message, which is used for switching off, to the EPC and completes the Detach process for switching off.
After having received the UE CONTEXT RELEASE COMMAND (IE Cause: Detach) sent from the EPC, the eNB cannot know the particular Detach Type (i.e., switch off or normal). Therefore, the eNB needs to send an RRC Connection Release message to the UE while releasing the UE related context information locally, so as to require the UE to release the UE context.
As described above, in the situation that the Detach Type is switch off, the UE can automatically release the UE context in local after having waited for a certain machine time period. Therefore, the eNB does not need to send the RRC Connection Release message, and if the eNB still sends the RRC Connection Release message in this case, the signaling overhead will be caused to increase on the contrary and the message retransfer may be caused, and thereby precious radio resources will be wasted.